2013 Fall Medium Range Discussion

[am19psu]

Since it's November 1, I thought it would be worthwhile to get this thread started again. There a New England threat for late next week already on the agenda. With MJO in P2-P4 for the next two weeks, but a strong -NAO, there is some chance of coastal lows, but overall, we're looking at cool weather on the coasts with warmth in center part of the country, but lower than climo chance for snow in the East.

[Ginx snewx]

Since it's November 1, I thought it would be worthwhile to get this thread started again. There a New England threat for late next week already on the agenda. With MJO in P2-P4 for the next two weeks, but a strong -NAO, there is some chance of coastal lows, but overall, we're looking at cool weather on the coasts with warmth in center part of the country, but lower than climo chance for snow in the East.

Weenie maps from the Euro this morning. Glad you started this thread again, it was a go to last year. Thanks. The persistence of the -NAO in the mid term is encouraging.

[am19psu]

This thread has been inactive, but if you're interested in medium range forecasting, pages 84-87 of the Winter 2012-2013 in the New England subforum have had excellent discussion about the next month.

[Srain]

The long range Euro and GFS are beginning to raise an eyebrow...

[am19psu]

Yeah, we've got a boring week to ten days to get through before the interesting things start to happen

[donsutherland1]

Last winter saw a lot of discussion in the thread dedicated to medium- and longer-range thoughts for the winter despite what turned out to be an abysmal winter for many of us. I will be starting a thread dedicated to the coming winter. In this initial message, my winter 2012-13 thoughts are provided.

Overall, I expect winter 2012-13 to experience below normal and near normal readings across the eastern third of the United States, as well as central Ontario and central Quebec southward. Alaska and adjacent areas in Canada will likely wind up colder than normal. The Pacific Northwest will likely experience near normal temperatures for the winter. The remainder of the U.S., along with northern Canada and Canada’s Atlantic Provinces will likely see warmer than normal readings. Northern Canada and the Desert Southwest could have the warmest anomalies.

Snowfall should return to near normal figures for the Great Lakes, Ohio Valley, northern Mid-Atlantic, and southern New England regions. Unlike last winter, the potential exists for a Kocin-Uccellini-type snowstorm at some point during the winter on account of the blockiness.

In terms of precipitation, the western half of the U.S. and southern Canada will likely see near to above normal precipitation. The Gulf Coast and Southeastern States could see below normal precipitation.

Last year saw a powerful positive Arctic Oscillation (AO+) become the primary synoptic driver. This winter, no single teleconnection appears likely to predominate. However, the potential for significant blocking suggests that the AO will probably be a major player.

Key Assumptions:

• Borderline-to weak El Niño conditions through much of the winter

• PDO- (near neutral PNA signal for the winter)

• A blocky winter with the potential for several extended periods of substantial blocking (AO)

At this point in time, there are some encouraging signals that lend confidence in the overall winter idea, despite a grim CFSv2 forecast.

Blocking:

The summer AO averaged -0.163. Since 1950, there were 38 cases during which the summer AO averaged < 0. 26/38 (68.4%) saw the winter AO also average < 0.

In cases when the summer AO averaged < 0, a winter AO < 0 was 1.4 times more likely than an AO > 0 during El Niño events. Winter 2009-10 was the most recent El Niño case that saw a negative winter AO.

In contrast, during those 38 cases, a winter AO > 0 was 2.9 times more likely than an AO < 0 during a La Niña. Winter 2011-12 was the most recent La Niña case that saw a positive winter AO.

More recently, the AO averaged -1.514 during October. Since 1950, there were 8 prior cases during which the AO averaged -1.000 or below during October. 6/8 (75%) saw the winter AO average < 0.

From that pool of 8 cases, 4 saw the AO fall to -2.000 or below during the December 1-10 period, as is forecast to occur by a majority of ensemble members.

All four (1966, 1981, 2002, and 2009) saw the AO average < 0 during the winter. 3/4 (75%) of those winters experienced a KU snowstorm. The exception (winter 1981-82) saw a springtime KU snowstorm (the April 1982 blizzard).

Since 1950, there were 20 KU snowstorms during the December-February period when the ENSO Region 3.4 anomaly was > 0. 18/20 (90%) commenced when the AO was < 0. 13/20 (65%) commenced when the AO was -1.000 or below.

Regional Hint from November Snowfall(s)?:

To date, November 2012 has seen 4.7” snowfall in New York City. There were six such cases since 1869: 1882, 1892, 1896, 1898, 1938, and 1989. 5/6 (83%) saw an additional 24.5” or more of snow accumulate during the season and 4/6 (67%) saw 30” or more additional snow. The single exception was winter 1989-90, which came to an abrupt end after a cold, snowy start. Among the leading analogs appearing for December is 1968 and 1977. In addition, all four December cases (1958, 1977, 1980, and 1981) with an ENSO Region 3.4 anomaly between 0.00 and +0.75 and a December 1-10 AO reading that fell to -2.000 or below saw generally cold winters in the East, though January-February 1959 was mild in the Mid-Atlantic and Southeastern regions. Consequently, I am reasonably confident that winter 2012-13 is not likely to be a replay of 1989-90.

[am19psu]

Hi Don, thanks for posting. I merged your thread with the one that was already started for the winter.

[donsutherland1]

Hi Don, thanks for posting. I merged your thread with the one that was already started for the winter.

Many thanks for merging it. I hadn't seen the thread earlier.

[mrgolf]

Happy holidays everyone! Im kevin from memphis tn. This msg is for either don sutherland, usetobe, and HM. Got a few questions i would like answered. I know phases 8,1, and 2 are usually required for a colder pattern in the central and eastern US. When do you guys see it getting in them more favorable phases, if at all? Also, is the alutian ridge hurting us to get the colder weather in here, even though the ao/nao are trending more negative? Lastly, just curious on what type of pattern setup we actually need to get the ball rolling, if you will, on a colder regime? Thanks kevin.

[donsutherland1]

Happy holidays everyone! Im kevin from memphis tn. This msg is for either don sutherland, usetobe, and HM. Got a few questions i would like answered. I know phases 8,1, and 2 are usually required for a colder pattern in the central and eastern US. When do you guys see it getting in them more favorable phases, if at all? Also, is the alutian ridge hurting us to get the colder weather in here, even though the ao/nao are trending more negative? Lastly, just curious on what type of pattern setup we actually need to get the ball rolling, if you will, on a colder regime? Thanks kevin.

Currently, the MJO is in low amplitude, so it isn't exerting as much influence as might be typical were it in higher amplitude. That situation increases the prospect that the development of strong blocking, which is forecast, could lead to a pattern change after the first 7-10 days of December.

[Met1985]

Nice to see you posting again Don. Should be pretty interesting come this winter.

[WXeastern]

Thanks for all the hard work Don..I always enjoy your stats/forecasts/outlooks!

[Srain]

For those interested, Wes has a topic in the Central/Western sub forum regarding the medium range and the prolific rain and snow totals expected in California and the Pacific NW Region. Some areas may be measuring snow in the feet with flooding rainfall possible in the lower elevations making for the major weather headline for the upcoming week.

http://www.americanwx.com/bb/index.php/topic/37940-interesting-analog/

[donsutherland1]

The latest run of CFSv2 has taken a big step away from warm anomalies across much of the CONUS. It is now in closer alignment with the Euro ensembles (which favor the warmest anomalies over the Desert Southwest) and JAMSTEC.

The latest computer guidance on the Winter 2012-13 Forecast:

The CFSv2 still favors widespread warmth for December, despite the possibility of significant blocking. It should be noted that although the CFSv2 has demonstrated skill in its monthly forecasts within 10 days of the month for which it is forecasting, it can be off. Its October 31 forecast for November 2012 had widespread warmth and missed what will likely wind up being cold anomalies across much of the eastern U.S.

[usedtobe]

The latest run of CFSv2 has taken a big step away from warm anomalies across much of the CONUS. It is now in closer alignment with the Euro ensembles (which favor the warmest anomalies over the Desert Southwest) and JAMSTEC.

The latest computer guidance on the Winter 2012-13 Forecast:

The CFSv2 still favors widespread warmth for December, despite the possibility of significant blocking. It should be noted that although the CFSv2 has demonstrated skill in its monthly forecasts within 10 days of the month for which it is forecasting, it can be off. Its October 31 forecast for November 2012 had widespread warmth and missed what will likely wind up being cold anomalies across much of the eastern U.S.

December will be interesting as the D+11 analogs certainly would start off the month warmer than normal despite the strongly neg ao because of the placement of the positive anomaly and the neg pna which helps pull warm air into the conus. Most model skill is probably in the 1st half of the month so I wouldn't be surprised if the CFS2 was on the right track though if the ridge in the pac retrogrades a little and then the trof along the coast retrogrades, the pattern could become quite cold.

[WXheights]

The latest run of CFSv2 has taken a big step away from warm anomalies across much of the CONUS. It is now in closer alignment with the Euro ensembles (which favor the warmest anomalies over the Desert Southwest) and JAMSTEC.

The latest computer guidance on the Winter 2012-13 Forecast:

The CFSv2 still favors widespread warmth for December, despite the possibility of significant blocking. It should be noted that although the CFSv2 has demonstrated skill in its monthly forecasts within 10 days of the month for which it is forecasting, it can be off. Its October 31 forecast for November 2012 had widespread warmth and missed what will likely wind up being cold anomalies across much of the eastern U.S.

Can anyone point me to any discussion about the new NMME and IMME ensembles theya have been developing? Per their info here --

"The multi-model ensemble approach has proven extremely effective at quantifying prediction uncertainty due to uncertainty in model formulation, and has proven to produce better prediction quality (on average) than any single model ensemble. This multi-model approach is the basis for several international collaborative prediction research efforts, including an operational European system. There are numerous examples of how this multi-model ensemble approach yields superior forecasts compared to any single model.

Based on two NOAA Climate Test Bed (CTB) NMME workshops (February 18, 2011 and April 8, 2011) a collaborative and coordinated implementation strategy for an NMME prediction system has been developed and is currently delivering real-time seasonal-to-interannual predictions on the NOAA Climate Prediction Center (CPC) operational schedule. The hindcast and real-time prediction data is readily available and in graphical format from CPC. Moreover, the NMME forecast are already currently being used as guidance for operational forecasters.

The Phase-I NMME project in 2011 was funded as a CTB Project by NOAA Climate Program Office Modeling, Analysis, Predictions and Projections (MAPP) Program. The Phase-II NMME project was funded as a 2-year (2012-2013) inter-agency project by NOAA, NSF, DOE and NASA."

I'ts got some "OMG projections" that look like - well huge polar amplification AGW for the winter and beyond. I do not know yet what to make of it but I'm sure there are others who zone in like yourself Don and have some thoughts on this. Make sure you are sitting down when peeking at the graphics...

[donsutherland1]

Can anyone point me to any discussion about the new NMME and IMME ensembles theya have been developing?

It seems that in recent years, regardless of whether the AO is positive or negative, the Arctic remains anomalously warm. It is warmer with an AO-. Given my thoughts that the AO will likely be predominantly negative, the warmth showing up on some of those maps is probably a reasonable idea.

[griteater]

Can anyone point me to any discussion about the new NMME and IMME ensembles theya have been developing?

Here you go - http://www.cpc.ncep.noaa.gov/products/NMME

[donsutherland1]

If one takes a look at the latest CFSv2 forecast for December, one finds coast-to-coast warmth in the U.S. Some of the warmth is quite impressive. On that model, the cold remains locked in Alaska and western Canada. The operational GFS is also warm through a large part of its extended forecast range.

However, the ensemble guidance has persistently been calling for a period of strong to possibly severe blocking to develop. The GFS ensembles take the AO below -2 with some members approaching or reaching -4 by the beginning of December. Consistent with that guidance, the AO turned negative today (-0.970). If severe blocking unfolds, December is not likely to feature coast-to-coast warmth in the U.S. Instead, a pattern change to colder is likely to develop, with the transition probably commencing sometime during the second week of December.

Going into the first week of December, analog timeframes include the December 1-6, 1977 and December 7-9, 1980 timeframes. The major difference is that the Arctic is much warmer than had been the case then, hence one reasonably should not expect an identical outcome. Nonetheless, one should expect the development of a colder pattern down the road.

But what about the CFSv2's toasty forecast? The below tables show that model's forecast for November (from October 31) vs. the actual outcomes to date.

In sum, the warm CFSv2 forecasts at the present time do not necessarily mean that a pattern change to colder is unlikely anytime soon.

[Ottawa Blizzard]

It seems that in recent years, regardless of whether the AO is positive or negative, the Arctic remains anomalously warm. It is warmer with an AO-. Given my thoughts that the AO will likely be predominantly negative, the warmth showing up on some of those maps is probably a reasonable idea.

Don, I regularly check the Environment Canada five day forecasts and it looks like the arctic is actually quite cold at the moment, with below average temperatures. In fact, would it not be safe to assume that Hudson Bay and James Bay may freeze earlier than they did last year?

[donsutherland1]

Don, I regularly check the Environment Canada five day forecasts and it looks like the arctic is actually quite cold at the moment, with below average temperatures. In fact, would it not be safe to assume that Hudson Bay and James Bay may freeze earlier than they did last year?

Ottawa Blizzard,

I was referring to the general relationship of the Arctic and the AO, not the state of the Arctic at the current point in time. Both AO outcomes now typically see more warmth than had previously been the case.

[Harry]

If one takes a look at the latest CFSv2 forecast for December, one finds coast-to-coast warmth in the U.S. Some of the warmth is quite impressive. On that model, the cold remains locked in Alaska and western Canada. The operational GFS is also warm through a large part of its extended forecast range.

However, the ensemble guidance has persistently been calling for a period of strong to possibly severe blocking to develop. The GFS ensembles take the AO below -2 with some members approaching or reaching -4 by the beginning of December. Consistent with that guidance, the AO turned negative today (-0.970). If severe blocking unfolds, December is not likely to feature coast-to-coast warmth in the U.S. Instead, a pattern change to colder is likely to develop, with the transition probably commencing sometime during the second week of December.

Going into the first week of December, analog timeframes include the December 1-6, 1977 and December 7-9, 1980 timeframes. The major difference is that the Arctic is much warmer than had been the case then, hence one reasonably should not expect an identical outcome. Nonetheless, one should expect the development of a colder pattern down the road.

But what about the CFSv2's toasty forecast? The below tables show that model's forecast for November (from October 31) vs. the actual outcomes to date.

In sum, the warm CFSv2 forecasts at the present time do not necessarily mean that a pattern change to colder is unlikely anytime soon.

Good discussion Don.

Here is a closer look for the lower 48 month to date temps..

Now here was Nov 2008. I have seen a few mention 08-09.

It is the best match i can find as well. Whether or not that means anything going forward remains to be seen.

[Srain]

For those interested, Wes has a topic in the Central/Western sub forum regarding the medium range and the prolific rain and snow totals expected in California and the Pacific NW Region. Some areas may be measuring snow in the feet with flooding rainfall possible in the lower elevations making for the major weather headline for the upcoming week.

http://www.americanwx.com/bb/index.php/topic/37940-interesting-analog/

Bump...The overnight guidance has come into better agreement with suggested liquid QPF from SFO into the Sacramento Valley/Sierra Nevada Range on northward increasing to the 10-15 inch liquid equivalent range or even higher. Gale Watches also have been hoisted along the N CA/OR Coastal areas. Guidance suggest that as the week moves forward, Coastal rains/mountain snow levels with increase northward as Pacific moisture floods inland with various short wave activity embedded within the long fetch moisture flow reaching near or just S of Seattle this coming weekend making for the major weather headline for the upcoming week across the US.

[OSUmetstud]

November daily AO less than -3.0 and the winters that followed.

36 of 53 winter months (Dec through March) that followed featured a negative average AO (67.9%)

The mean monthly AO that followed was -0.840

1950-1951, 1952-1953, 1955-1956, 1957-1958, 1959-1960, 1962-1963, 1965-1966, 1968-1969, 1972-1973, 1984-1985, 1985-1986, 1998-1999, 2002-2003

Washington Baltimore NYC(Central Park) Boston

Mean 17.5" 22.2" 22.6" 38.0"

1981-2010 Normal 15.4" 20.1" 25.1" 43.7"

[donsutherland1]

Arctic Oscillation Now Diving...

This morning, the Arctic Oscillation (AO) stood at -1.956. Strong to possibly severe blocking that had persistently been modeled appears now to be developing. If some of the ensemble members are right, the AO will likely fall below -3.000 during this blocking episode. Some ensemble members take the AO below -4.000.

Severe blocks that commence in late November/early December can be long-lived. Notable long-lived blocks have developed in that timeframe following a blocky October. In other words, the blockiness that was present in mid-Autumn reasserted itself during the winter.

Recent examples include the blocking regimes of 2009-10 and 2010-11. The following severe blocking episodes (minimum AO value of -3.000 or below) began in late November/early December (11/20-12/10) following a blocky October (monthly AO of -025 or below):

December 7, 1966-January 11, 1967: 36 days

December 7, 1981-January 12, 1982: 37 days

November 29, 2009-January 15, 2010: 48 days

December 3, 2010-January 15, 2011: 44 days

In contrast, the severe blocks that developed during the same timeframe, but did not follow a blocky autumn (neutral or positive AO) were often shorter-lived. In cases, they were more an anomaly in a longer-term pattern that featured less blocking. However, some of those patterns eventually became blocky. Winters 1977-78 and 1995-96 were examples.

Those blocks were:

December 4, 1958-December 27, 1958: 24 days

December 6, 1961-December 13, 1961: 8 days

December 2, 1977-December 11, 1977: 11 days

December 3, 1989-December 21, 1989: 19 days

December 5, 1995-January 8, 1996: 35 days

December 6, 1996-January 12, 1997: 38 days

November 27, 2001-January 1, 2002: 36 days

Using all 11 cases, one finds:

Mean duration: 30.5 days (standard deviation: 13.1 days)

Median duration: 36.0 days

Less than 7 days: 0/11 (0%) cases

Less than 14 days: 2/11 (18%) cases

20 days or longer: 8/11 (73%) cases

30 days or longer: 7/11 (64%) cases

40 days or longer: 2/11 (18%) cases

Given the development of what might be long-lived blocking, the evolution of a colder regime across the eastern third or even eastern half of the U.S., as well as southern Ontario and southern Quebec appears likely down the road. The transition could occur during the second week of December.

In its most recent weekly data, the CFSv2 is now showing this transition:

In the meantime, beginning Wednesday, a 5-7-day siege of precipitation is poised to inundate the Pacific Northwest. With the extreme precipitation figures modeled and the long-duration involved, this event is likely to be one of the highlight events of late fall 2012-winter 2013.

This post has been promoted to an article

[uncle W]

Arctic Oscillation Now Diving...

This morning, the Arctic Oscillation (AO) stood at -1.956. Strong to possibly severe blocking that had persistently been modeled appears now to be developing. If some of the ensemble members are right, the AO will likely fall below -3.000 during this blocking episode. Some ensemble members take the AO below -4.000.

Severe blocks that commence in late November/early December can be long-lived. Notable long-lived blocks have developed in that timeframe following a blocky October. In other words, the blockiness that was present in mid-Autumn reasserted itself during the winter.

Recent examples include the blocking regimes of 2009-10 and 2010-11. The following severe blocking episodes (minimum AO value of -3.000 or below) began in late November/early December (11/20-12/10) following a blocky October (monthly AO of -025 or below):

December 7, 1966-January 11, 1967: 36 days

December 7, 1981-January 12, 1982: 37 days

November 29, 2009-January 15, 2010: 48 days

December 3, 2010-January 15, 2011: 44 days

In contrast, the severe blocks that developed during the same timeframe, but did not follow a blocky autumn (neutral or positive AO) were often shorter-lived. In cases, they were more an anomaly in a longer-term pattern that featured less blocking. However, some of those patterns eventually became blocky. Winters 1977-78 and 1995-96 were examples.

Those blocks were:

December 4, 1958-December 27, 1958: 24 days

December 6, 1961-December 13, 1961: 8 days

December 2, 1977-December 11, 1977: 11 days

December 3, 1989-December 21, 1989: 19 days

December 5, 1995-January 8, 1996: 35 days

December 6, 1996-January 12, 1997: 38 days

November 27, 2001-January 1, 2002: 36 days

Using all 11 cases, one finds:

Mean duration: 30.5 days (standard deviation: 13.1 days)

Median duration: 36.0 days

Less than 7 days: 0/11 (0%) cases

Less than 14 days: 2/11 (18%) cases

20 days or longer: 8/11 (73%) cases

30 days or longer: 7/11 (64%) cases

40 days or longer: 2/11 (18%) cases

Given the development of what might be long-lived blocking, the evolution of a colder regime across the eastern third or even eastern half of the U.S., as well as southern Ontario and southern Quebec appears likely down the road. The transition could occur during the second week of December.

In its most recent weekly data, the CFSv2 is now showing this transition:

In the meantime, beginning Wednesday, a 5-7-day siege of precipitation is poised to inundate the Pacific Northwest. With the extreme precipitation figures modeled and the long-duration involved, this event is likely to be one of the highlight events of late fall 2012-winter 2013.

great post Don...With strong blocking and plenty of Pacific moisture we could be seeing some record snowfalls across the country in December...1979 had a low October AO value but it became quite positive in November/December...This year the AO is already much lower...If the AO dips below -4.000 we could be in for some deep snows or record cold in the NYC area...

[OSUmetstud]

great post Don...With strong blocking and plenty of Pacific moisture we could be seeing some record snowfalls across the country in December...1979 had a low October AO value but it became quite positive in November/December...This year the AO is already much lower...If the AO dips below -4.000 we could be in for some deep snows or record cold in the NYC area...

Why? The data shows -AO winters which follow low November AOs are a mixed bag.

[donsutherland1]

November daily AO less than -3.0 and the winters that followed.

36 of 53 winter months (Dec through March) that followed featured a negative average AO (67.9%)

The mean monthly AO that followed was -0.840

1950-1951, 1952-1953, 1955-1956, 1957-1958, 1959-1960, 1962-1963, 1965-1966, 1968-1969, 1972-1973, 1984-1985, 1985-1986, 1998-1999, 2002-2003

Washington Baltimore NYC(Central Park) Boston

Mean 17.5" 22.2" 22.6" 38.0"

1981-2010 Normal 15.4" 20.1" 25.1" 43.7"

Filtering the above data for December-February average ENSO Region 3.4 values one finds:

DJF Average > 0:

Baltimore: 27.6"

Boston: 41.7"

New York City: 27.3"

Washington, DC: 21.1"

DJF Average: Positive but less than +1.5:

Baltimore: 30.3"

Boston: 48.9"

New York City: 29.0"

Washington, DC: 21.6"

[OSUmetstud]

Filtering the above data for December-February average ENSO Region 3.4 values one finds:

DJF Average > 0:

Baltimore: 27.6"

Boston: 41.7"

New York City: 27.3"

Washington, DC: 21.1"

DJF Average: Positive but less than +1.5:

Baltimore: 30.3"

Boston: 48.9"

New York City: 29.0"

Washington, DC: 21.6"

How about just a neutral filter? There's probably some solid weak/moderate Nino years that could be contaminating the data set.

[OSUmetstud]

2 out of the 13 years were neutral years.

Washington: 18.0"

Baltimore: 17.6"

NYC: 14.7"

Boston: 24.5"

These two years did feature strong AO blocking, so that wasn't the issue. My general point is the AO isn't as important to winter snowfall as one might think.

Btw, this was 1962-1963 and 1985-1986